Typical projection systems include a source of light, illumination optics, one or more image-forming devices, projection optics and a projection screen. The illumination optics collect light from one or more light sources and direct that light in a predetermined manner to one or more image-forming devices. The image-forming devices, controlled by an electronically conditioned and processed digital video signal or by other input data, produce images corresponding to the video signal or to that data. Projection optics then magnify the image and project it onto the projection screen. White light sources, such as arc lamps, in conjunction with color-maintaining systems, have been and still are predominantly used as light sources for projection display systems. However, recently, light emitting diodes (LEDs) were introduced as an alternative. Some advantages of LED light sources include longer lifetime, higher efficiency and superior thermal characteristics.
Examples of image-forming devices frequently used in projection systems include digital micro-mirror devices, or digital light processing devices (DLPs), liquid crystal on silicon devices (LCoS) and high temperature polysilicon liquid crystal devices (HTPS-LCD). Illumination optics of common projection systems often include integrators. Integrators typically serve to homogenize light supplied into their input ends via reflections at the integrators' walls. Presently known integrators include mirror tunnels, for example, rectangular tunnels, solid or hollow, and elongated tunnels composed of solid glass rods that rely on total internal reflection to transfer light.